541 
Tivo Fluids, and of Two Metals not in Contact, 
sulphuric acid and towards hydrochloric acid ; in the whole, 
therefore, 34 cases. In 18 cases the acid had the preponderance ; 
in 10 the iodide of potassium. In 6 the result was ambiguous, 
as during the experiment a decided reversion of the current en- 
sued; and probably some of the first belong to this category. 
If we merely look at the number of favourable cases, the affi- 
nity-theory would indeed still retain some probability ; but this 
must entirely disappear if at the same time we take into consi- 
deration the iveight of the unfavourable cases. 
Among the latter, viz. the unfavourable cases, those with 
platina more especially surprised me, and of these that with 
the combination zinc-platina and hydrochloric acid. It is in 
fact the same experiment which Faraday mentions in support 
of his view, which he himself had the kindness to show me in 
London (in this experiment hydrochloric acid was employed), 
and which I also had previously more than once performed 
with the same positive result. Whence now the opposite re- 
sult ? Am error it could not be ; I had repeated it so often 
and under the most varied circumstances ! After some expe- 
riments I was so fortunate as to find the solution of this enigma ; 
and with this, at the same time, the untenability of the expla- 
nation of the experiment, as also of the whole of this argument 
in favour of the chemical theory of Galvanism, is, in my opinion, 
clearly demonstrated. 
The result of the experiment, in fact, depends solely on the 
concentration of the acid*. If we employ, as was the case in all 
the experiments enumerated in the table, a hydrochloric acid 
of 1T38 spec, gr., diluted with 6 times its volume of water, the 
iodide of potassium has the preponderance ; but if, on the con- 
trary, the same acid be employed but not diluted, the superiority 
is then on the side of the acid ; and the current has such a direc- 
tion, that on the decomposition of the iodide of potassium, the 
iodine passes to the platina. Between these two degrees of 
concentration of the acid, there will evidently be one with which 
not the least current will occurf. 
* Probably also on the concentration of the solution of the'iodide of potassium ; 
but I have not varied this. — On the other hand, I have assured myself, that 
the purity of this solution has little influence. A solution which from frequent 
use was mixed with sulphuric acid, had thus become brown and acid, and con- 
tained therefore free hydriodic acid with iodine, and dissolved zinc with effer- 
vescence, — acted just the same as pure iodide of potassium, and evinced with 
platina the superiority over hydrochloric acid more strongly than the latter. 
f Likewise with silver, copper, and' tin, combined with amalgamated zinc, 
the concentrated hydrochloric acid (of 1-138 spec, gr.) has instantaneously 
and strongly the ascendency over the iodide of potassium ; even the diiute acid 
with silver and copper acts in the same way, as shown in the table ; with tin, 
however, it succumbs to the iodide of potassium. The action of tin is there- 
fore quite analogous to that of platina. 
